MOUNTING AND PREPARATION OF OBJECTS. 43 



sam mounts, are suitable for microscopic plants and 

 other objects which it is desirable to examine without 

 removing all the water which they contain. Some pre- 

 liminary treatment is necessary even in this case, since 

 cells containing a large amount of water, if placed di- 

 rectly in a strong solution of glycerin, would be torn and 

 distorted by the violent diffusion currents set up. The 

 most , convenient way to prepare such objects is to im- 

 merse them in io% glycerin and set them by for a few 

 (^ays under cover, as a protection from dust, so that the 

 water may evaporate and produce a gradual concentra- 

 tion of the glycerin. 



Specimens thus prepared may be mounted in a deep 

 cell filled with pure glycerin, but it is a difficult matter to 

 cover the cell so that air-bubbles shall not be included, 

 and a still more difficult matter to cement the cover 

 firmly to the wetted surface of the ring. For most pur- 

 poses glycerin jelly * is much more convenient, since 

 this substance becomes solid on cooling and obviates 

 the necessity for a cell or for cement to attach the cover - 

 slip. All that is necessary in using this medium is to 

 melt it by gentle warmth, cover the object with a good- 

 sized drop of it, put on the cover-slip, and set aside in a 

 cool place. 



6. Mounting in Balsam Media. — The most permanent 

 and satisfactory of all mounting media is Canada balsam, 



* One part of gelatin by weight is soaked in 6 parts of water 

 7 parts of pure glycerin are added and finally i% of phenol. The 

 mixture is warmed for ten to fifteen minutes, with constant stirring, 

 till it is clear and is then filtered. 



